Js写一个点名程序

Html

<button id="start">开始点名</button>
<button id="end">结束点名</button>
<div id="name"></div>

CSS

#name{
      width: 135px;
      text-align: center;
      padding-top:10px;
    }

JS

#name{
     window.onload = function () {
    var start = document.getElementById('start');
    var end = document.getElementById('end');
    var name = document.getElementById('name');

    var nameArr = ['Leon','Allen','Ella','Lee','Howard'];

    var timer = null;

    // 开始点名
    start.onclick = function () {

      // 清除定时器
      clearInterval(timer);

      // 设置定时器
      timer = setInterval(function () {

        // 设置随机数
        var s_index = parseInt(Math.random()*nameArr.length);
        var s_name = nameArr[s_index];
        console.log(s_name);
        name.innerText = s_name;

      },20)
    };

    // 结束点名
    end.onclick = function () {
      clearInterval(timer);
    }
  }
    }